1. Field of the Invention
The invention relates to a process for printing paper. More particularly, it relates to a process for printing using a solution containing one or more water-soluble polymeric dyes.
2. Background and Prior Art
With but minor exceptions, water-fastness of printed materials, especially printed paper, is a desired property. Historically, water-fastness has been achieved by using inks that are solutions or suspensions in oil or organics of water-insoluble pigments and/or dyes. Two factors have rendered obsolete this previous approach. The first factor is increasing concern about the release of toxic organic vapors into the workplace and environment. This limits or prohibits the use of materials which, upon drying, release these organics (for example, benzene). The second is the introduction of new high-speed printing and coloring methods, such as those employing variable orifice spraying, which require true solutions of color as opposed to suspensions or pastes. The present invention employs solutions of dye in water-based solvent systems to address these new factors.
The present invention also employs polymeric colorants. A "polymeric colorant" is expressly defined to be a colorant having a plurality of chromophore units covalently linked together by a nonchromophoric backbone or by intermediate linking groups, into a single molecular unit. Polymeric colorants per se are, of course, known in the art. We and our coworkers have disclosed a range of such materials in patents and publications. See, for example, U.S. Pat. No. 3,920,855, issued Nov. 18, 1975 to Dawson and Rudinger; U.S. Pat. No. 4,018,826, issued Apr. 19, 1977 to Gless, Dawson and Wingard; U.S. Pat. No. 4,096,134, issued June 20, 1978 to Otteson and Dawson; U.S. Pat. No. 4,144,252, issued Mar. 13, 1979 to Wang and Wingard; and U.S. Pat. No. 4,182,885, issued Jan. 8, 1980 to Bunes, as representative disclosures of various polymeric colorants based on nonchromophoric backbones. These references generally focus on the preparation of polymeric colorants and on the colorants themselves. While they do not preclude other uses, they do not suggest the present process. Another reference of interest is U.S. Pat. No. 3,337,288, issued Aug. 22, 1967 to Horiguchi and Nakamura which discloses an alleged polymeric colorant, which may in fact be pigment-like in character, and its use as a printing ink component. This reference, as well, does not disclose nor suggest the present invention, which is based on the achievement of water-fast print using true solutions of water-soluble dyes.